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Re: Notes on 2.4 GHz beacon



There's a good explanation in the Satellite Handbook of Squint Angle. I
don't have it with me as I'm at work, but it goes like this:

If the sat goes directly overhead (very rare), with your antenna pointing
right at it, and its antenna pointing directly at you, there's zero squint:
a Truly circular pattern from the sat will appear truly circular on the
ground.

As the sat approaches the horizon, it's pointing directly down at another
point on the earth. The pattern will appear to become more linear to you (or
to look at it another way, eliptical). A bit like if you look at a hoop and
turn it you'll eventually see it become a straight line as it moves from
circle, then elipse.

This is where stacked or physically separated antennas start having
particular problems too especially if they're not pointing straight at the
sat, even tough their beamwidths may be quite wide.

The wavefronts from the sat to each antenna in the array will be offset by
an angle if the antennas aren't pointing straight at the satellite. These
wavefronts can, if the antennas are far enough apart (wavelength wise)
and/or at a sufficient angle away from pointing directly to the satellite,
appear to cancel each other out or even reverse polarization if the antennas
are mounted perpendicularly.

The latter case can be rectified somewhat by regularly updating the antenna
position, producing more wear on the rotor.

73 Howard G6LVB

----- Original Message -----
From: "Jon Ogden" <na9d@mindspring.com>
To: "Gene Harlan" <atvq@hampubs.com>; <amsat-bb@AMSAT.Org>
Sent: Friday, December 01, 2000 5:06 AM
Subject: Re: [amsat-bb] Notes on 2.4 GHz beacon


> on 11/29/00 11:07 PM, Gene Harlan at atvq@hampubs.com wrote:
>
> > What is squint angle? I can't say I've heard that term before and now
> > everyone seems to be using it! If I were to guess I would say it is beam
> > width of the antenna?
>
> I think it's the angle between your antenna and the main lobe of the
> satellite's antenna.   If the satellite antenna is pointing straight at
your
> antenna, the squint angle is zero.  If the satellite's antenna is pointing
> in a direction 90 degrees away from you, the squint angle is 90 degrees.
>
> I *think* that's what this is.
>
> If you have a squint angle other than zero or close to it, you'll be off
the
> main beam of the satellite's antenna.  This can obviously making hearing
> difficult.  In the case of the 2.4 GHz beacon tests, the control team has
> chosen the point in the orbit when the satellite's antennas are most
pointed
> toward earth and hence the smallest squint angle.
>
> 73,
>
> Jon
> NA9D
>
> -------------------------------------
> Jon Ogden
> NA9D (ex: KE9NA)
>
> Member:  ARRL, AMSAT, DXCC, NRA
>
> http://www.qsl.net/ke9na
>
> My President is George W. Bush -> The legal winner in Florida
>
> ----
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>

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